What Is GPS? And How Does It Work?

The "Global Positioning System" is a satellite navigation system developed and owned by the United States Department of Defense. Between 24 and 32 satellites circle the Earth and send signals to receivers on the ground, which then use those signals to determine their location, speed, direction and time. In-car satellite navigation uses basic GPS readings (longitude and latitude) along with roadmap data.

Consider The Size And Look Of The Display Screen

Currently, car GPS units are available in four sizes (screens are measured diagonally): 3.5-inch, 4.3-inch, 4.7-inch and 5-inch. Generally, bigger is better, but in the case of small cars, consider a screen size that won't obstruct too much of your view. Choose a glare-free display that's clear and easy to read in daylight.

Maps: Suppliers, Displays And Updates

On-screen graphics play a big part in the appeal of a sat nav unit. GPS maps should be displayed as two\- or three-dimensional and easy to follow, with information such as "distance to next turn," "current street name" and "points of interest" (POI) like airports, hospitals, petrol stations and so on.

The latest version of a map is normally supplied with your new GPS. Of course, roads and transport infrastructure change over time, so maps will eventually date and you may need to buy revised ones. A good GPS system should offer local and overseas map updates for download, usually by linking to a computer via a USB connection. Many sat nav units have some form of internal memory, as well as SD card slots, for storing and updating information.

Some Extra Features To Consider

Text-to-Speech Capability: Spoken directions using specific street names --- "turn left in 30 metres on to Geylang Street" --- rather than generic instructions make for safer navigation. Voice instructions should be clear and loud enough to hear over any background noise in your car.

Lane Guidance: Gives you instructions to make lane changes on the road ahead. Advance warnings are useful, especially during peak-hour traffic and for places with multiple lanes, like freeways and airports.

Safety Camera Alerts: Red light and speed camera alerts help reduce stress by alerting you of hotspots while travelling. Some GPS units also include warnings for school zones. Don't rely completely on safety camera alerts because they're not fail-safe --- for example, alerts are on 24/7, instead of the relevant times during school days.

Routing: Works out the best route between locations and customises the trip --- for example, choosing a way that avoids tolls.

Road Sign Display: Shows the main road signs on your journey.

Stay On Track With Live Traffic Reports

Real-time traffic information --- including the location of accidents and likely delays --- is available for many sat nav units. Keep in mind, the service can be prone to delays and not all roads are covered.

Easy Installation And Portability Are Key

Your GPS unit sits in a cradle, which is mounted to the inside of the car's windscreen via a suction cup and within your line of vision. One of the main advantages of a GPS unit is the portability. An in-car GPS should be easy to attach and remove. Tip: When leaving your car, wipe away any marks left on the windscreen by the GPS cradle's suction cup; these are a sign to would-be thieves that there may be a GPS unit hiding in the glovebox.

The Antenna And Its Reception

How well an in-car GPS unit works depends on where its antenna is located; most portable sat navs are placed directly on the windshield. GPS systems work most effectively with a clear view of the sky, so they can "see" the satellites better. They can struggle whenever obstructed, for instance, amongst the tall buildings of a Central Business District. Add-on antennas can be mounted at the base of your windshield to improve signal reception.

What Is Bluetooth? Do I Need It?

Bluetooth is short-range, wireless technology used for connecting and transferring information between devices. A GPS with Bluetooth can double up as a hands-free speaker when connected to a Bluetooth-equipped mobile phone.

Tip: Some GPS units have Bluetooth profiles that aren't compatible with certain mobiles, so make sure your phone and Sat Nav match.

Never Run Out Of Power

When fully charged, expect between three to five hours of battery life. Consider buying additional battery packs, so you're never left stranded. For continuous power or recharging the battery in-car, GPS units use a 12V power socket, usually the one that houses the cigarette lighter.

It's A Multimedia Device, Too

Many GPS systems now offer media playback --- you can view photos, listen to music and watch video --- usually from an SD flash card. Keep in mind that video and photo playback might not be very practical on a small screen; satellite navigation units usually suffer from poor screen resolution and limited processing power.

Make sure your sat nav unit has either an FM transmitter or a 3.5mm line-out jack so you can listen to music through your car's stereo --- rather than the GPS's speaker --- for better sound quality.